Some counties in the nation are too small to have reliable measurements for health outcome measures. Those counties are not ranked. If a county has data for enough measures to be ranked but is missing data for any individual measure, we assign the county the same value as the state mean for that measure. One way to overcome unstable and unreliable estimates due to small numbers, such as with the measures from the Behavioral Risk Factor Surveillance System (BRFSS), is to combine multiple years of data. This means that although the Rankings are useful for differentiating between places that are and are not healthy, they are not a good tool for setting objectives and tracking progress from year to year.